Own work. Geometry based on description in DPRK National Flag Law 2014-08-12 which can be found at www.unilaw.go.kr.

Appendix 1 — Ratio between the width of the national flag and the diameter of the red star, the center point of the white circle, the white circle, and the red star

1. The national flag is divided vertically into 6 equal parts with both the upper and lower ¹⁄₆ being coloured blue, the remaining ⁴⁄₆ is divided vertically into 24 equal parts with both the upper and lower ¹⁄₂₄ being coloured white, the remaining ²²⁄₂₄ is coloured red.
2. The center of the red star, and the center of the white circle are both located at the intersection of the national flag's horizontal bisector and the vertical trisector on the side of the flagpole.
3. The diameter of the white circle is ²⁄₃ the vertical height of combined red and white parts of the national flag, the diameter of the imaginary circle that circumscribes the star is equal to the diameter of the white circle less ¹⁄₂ the thickness of one white stripe. The tips of the red star do not touch the perimeter of the white circle.
   — English translation of Appendix 1 from KPRK National Flag Law 2014-8-12

Another English translation can be found at Law and North Korea, but be warned that it mixes up the definitions of bisector and trisector.

See also:

• File:《조선민주주의인민공화국 법전(제2판)》(법률출판사).pdf, page 51
• File:Flag of North Korea (construction sheet by Kim Tu-bong).jpg